1. Technical Field
The present invention relates to a paper width detection method used in a label printer to accurately detect the paper width of a recording medium, a printing control method for a label printer for printing to a recording medium based on the paper width detected by said paper width detection method, and to a label printer.
2. Related Art
Printers that print to a recording medium such as label paper having labels affixed at a constant interval along a long web liner are known from the literature. Such printers detect the width of either the recording medium liner or the labels affixed thereto by a detection operation using a paper width detector disposed to the transportation path through which the recording medium is conveyed, and by control of the other parts of the printer for printing based on the detection result. An optical sensor is commonly used as the paper width detector, and the width of the liner portion or the label portion of the recording medium is detected by emitting a detection beam to the recording medium liner or label and detecting the light that passed through or the light that is reflected.
Japanese Unexamined Patent Appl. Pub. JP-A-2007-216515 teaches a printing device having an image sensor head and a reflector member disposed above and below the label paper. The image sensor head has optical elements arrayed at a density of 300 dpi, and the image sensor head and reflector are wider than the label width. This configuration emits a detection beam from the image sensor head toward the label paper and detects the light reflected from the reflector or from the label by the optical elements of the image sensor head to detect labels of different widths.
Methods that detect the recording medium width based on change in the reflectivity or transmittance when scanning across the width of the recording medium cannot differentiate the change in reflectivity or change in transmittance caused by punch holes, soiling, or damage to the recording medium from a change in reflectivity or change in transmittance at the edge of the recording medium, and can therefore result in detection errors.
Furthermore, because the amount of light that is reflected back by the liner is low when the recording medium uses a transparent liner or a liner with low reflectivity, such as a black liner, the point where the reflectivity changes near the edge of the liner can be difficult to detect. The change in transmittance near the edge of the liner can also be difficult to detect with a recording medium that has a liner with high transmittance, such as a transparent liner. Erroneous detection or a detection error reporting that the edge of the recording medium could not be detected may therefore result.
If the label paper has the labels affixed to a liner for which the edges can be difficult to detect, the likelihood of being able to detect at least the width of the labels is high if the paper width detection process is executed when the labels are at the paper width detection position. However, if the paper width is detected when the gap between labels (the portion of the liner between adjacent labels) is at the paper width detection position, the edges of the liner and the edges of the label cannot be detected, and an error reporting that the paper width could not be detected may result.
In the case of die-cut labels, cuts and voids can be formed by the die around the labels as a result of the stamping process. The reflectivity therefore changes sharply in such voids, and the void may be falsely detected as the edge of the liner. The likelihood of such detection errors is particularly high with die-cut label paper when the labels are affixed to a liner for which detecting the edges can be difficult, such as a transparent liner or black liner. In such situations the width of only the part (that is, the waste matrix part, the excess portion left after the labels are removed in the production process) of the liner on the left and right sides of the label may be wrongly detected as the width of the recording medium.